The invention relates to an electrical switch with a thermostatic working element as an actuating element, and with a switch element designed as a microswitch, said elements being mounted in a one-piece metal housing with a round cross section, open on one side, said housing having a recess in its bottom area to accept a substance, especially wax, which expands when heated, said recess being covered by a rubber-elastic membrane, upon which membrane a working piston made of an insulating material, especially plastic, which is displaceable as a function of an expansion of the material, is mounted, said piston being guided in a fixed guide part which holds the membrane and comprises an axial bore, said piston being located opposite one end of a rocker of the microswitch, said rocker being aligned in an output position at an angle to the displacement direction of the working piston, said rocket being mounted on a support, and pivotable about an axis running at right angles to the displacement direction of the working piston, said rocker having its other end engaged by an extension spring serving as a restoring means for the working piston, said spring being attached to a contact tongue, said tongue being aligned essentially at right angles to the displacement direction of the piston and being mounted pivotably on the support, said tongue bearing a contact, said contact being located opposite a normally closed (NC) contact on one side and opposite a normally open (NO) contact on the other side, said contact being retained by a contact support, whereby a circular plate made of an insulating material, especially plastic, serves as a closure for the open side of the housing, said plate receiving the NC contact as well as the contact support of the NO contact and the support, and through which the electrical leads to the support and/or the contact carrier are fed to the exterior.
The known switches of the type recited hereinabove (German Pat. No. 2,444,931) are used primarily in the construction of motor vehicles and are used particularly for turning on the cooling fan of the engine cooling system when a certain engine temperature or coolant temperature is reached. In particular, the fact that the extension spring of the microswitch also serves as a restoring means for the working piston has made it possible to simplify the design and thereby considerably reduce the structural dimensions and the cost as well. Hence, switches of this type have already been used in many applications instead of switches which use a bimetallic strip as the switching element, especially since the switches with the thermostatic working element are much more reliable and exhibit higher operational reliability.
Known electrical switches with a bimetallic switch element, however, still have the advantage over known electrical switches with a thermostatic working element and a microswitch in that they are smaller and in some aspects can also be manufactured less espensively. Tests have shown that it is not possible to decrease the size of the known switch (German Pat. No. 24 44 931) by reducing its scale, largely because the space required for installing the microswitch cannot be significantly reduced.
Thus, a principal object of the invention is to design an electrical switch of the type recited hereinabove in such fashion that smaller dimensions are made possible, so that the amount of materials to be installed, and consequently the material cost and price, can be reduced accordingly, while retaining the basic principle thereof. This object is achieved in accordance with the present invention by virtue of the fact that the contact support of the NO contact, looking at the plate in the top view, is disposed laterally next to the contact tongue and mounted on the plate, displaced toward its center.
The invention is also based on the fact that a considerable limitation upon the dimensions of the microswitch that can be achieved results from the fact that the structural length of the extension spring cannot be reduced beyond a certain size for manufacturing reasons and also because of the necessary overtravel. The displaced arrangement of the contact support of the NO contact in accordance with the present invention, however, provides additional structural space precisely in the axial direction of the extension spring, so that the microswitch in particular can be made smaller.
One advantageous embodiment of the invention provides for the support and the contact support to be inserted in the plate and brought out of the latter as flat prongs, whereby the part of the contact support which forms the prongs, looking at the plate in a top view, is rotated 90.degree. relative to the support. This ensures that the prongs are readily accessible for connection.
In order reliably to anchor the support in the plate against the extension spring force, which serves as a restoring means, provision is also made for the support to be inserted in a recess in the plate by a rectilinear extension. In order to permit an advantageous electrical connection to the support, provision is also made for the part which serves as a prong and penetrates the plate to be connected to the side of the support and rotated 90.degree. thereto. This ensures that, despite the small dimensions, the two prongs, which are parallel to each other, will be readily accessible.
In another embodiment of the invention, provision is made for the microswitch to be provided with an outwardly projecting center contact (instead of two flat prongs), to which the contact support of the NO contact is connected, said support being riveted, with the projection which is located on the inside of the plate, to the center contact inserted into the plate. Additionally, the support has a projection which is inserted into the plate and a projection which lies on the inside of the plate, the latter projection extending outward as far as the edge of the plate and being connected in a conducting fashion with the housing.
In order further to reduce the space required for installation of the microswitch, one advantageous embodiment of the invention provides for the arm of the rocker, which the extension spring engages, to be bent in the direction of the support which projects perpendicularly from the plate. This permits reducing the space required for the rocker arm to swivel in the lateral direction.
In order either to permit an extension spring to have a greater length or further to reduce the structural dimensions, a further embodiment of the invention provides for the housing to have a first cylindrical part to accept the microswitch, against which a middle part, which has tool-application areas externally, especially an external hexagon, and accepts the guide part of the working piston internally, abuts, followed by an end part with inner and outer diameters that are smaller, said end part being provided with an external thread and having an internal recess for the substance which expands when heated. Thus, despite the transition to a relatively small thread, a sufficient volume is made available for the substance which expands when heated, and consequently the axial height of the housing can be made smaller on the whole.
In order to provide for the overtravel of the working piston which is required in practice because of the admissible temperature increases, despite the small dimensions, i.e., the travel which occurs after the switching has taken place, it is advantageous for the diameter of the working piston to be about 2/3 of the diameter of the recess for the substance which expands when heated.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.